Radiation detectors, particularly those that are responsive in the ultraviolet range, are useful as fire detectors in certain applications. This is due to the fact that the flame from a fire generates radiation that includes the ultraviolet region of the spectrum. The middle ultraviolet, in the range of 2000 to 2800 Angstroms, is not generally present in sunlight as it reaches the earth's surface but is well transmitted through air. The extreme or far ultraviolet, in the range of 100 to 2000 Angstroms, connects the ultraviolet and X-rays and is not transmitted through air. The useful range for the detection of radiation from fires, is, therefore in the middle ultraviolet, and detection equipment employing detectors with a peak response at approximately 2100 Angstroms has been in use for a number of years. These detectors will also respond to high energy radiation of other frequency levels, particularly that known as cosmic radiation.
Detectors of ultraviolet radiation commonly consist of metal electrodes sealed in an enclosure arranged to receive radiation of the desired intensity and which enclosures contain one or more readily ionizable gases. When radiation strikes this detector, and the radiation is of sufficient energy, the impedance of the detector will change and allow the transmission of current. Obviously the measure of this current flow will be significant to the amount of radiation received. Such detectors are known to have several modes of failure and various yesting arrangements have been developed to determine whether or not the same and their associated circuitry is capable of responding to radiation from a fire. Many of these testing systems have shortcomings in their useage and in order to overcome these problems, it has been found that the mounting of a source of radiation, in the proper range of emission, integrally with the detection unit is a partial approach to the reduction of tube failure problems and such units are well known in the art. However, this mounting does not provide for a solution to thorough, continuous and proper monitoring of all the various modes of failure of the system.
Applicants' invention is particularly related to improvements in systems for the continual monitoring of radiation detection systems and more particularly those useable in the ultraviolet region, whether the monitoring source of radiation is located externally to the radiation detector enclosure or whether the source of radiation is located within the same housing.
It is therefore an object of applicants' invention to provide a testing system and the associated circuitry for a radiation detection system which is functional and operable whether the source of radiation is positioned externally to the housing for the detection unit or the source of radiation is arranged within the same housing as the detection unit.
It is a further object of applicants' invention to provide a monitoring system and associated circuitry therefore which includes means for maintaining an actuation level of operation for the unit which compensates for outside radiation or spurious discharge factors.
It is a further object of applicants' invention to provide a constant and continuous monitoring system for a radiation detection system which includes a source of radiation and the controls therefore which are responsive to radiation being received by the detection unit.
It is still a further object of applicants' invention to provide a radiation detection unit which includes a controlled source of radiation and wherein the actuation of the source of radiation is monitored.